A friend has a jacket manufactured from some synthetic fabric in 1964. It was originally a steel blue color, but it is decaying into dark brown powder. It is a stretchy weave textile, but I don’t think it’s polyester, because I’ve seen racks of polyester neckties from the 1960s and 1970s (my dad’s) that haven’t decayed one bit.
Anyone have a guess on what fabric it is, and if anything can be done to stop the decay? It has a great sentimental value.
Not sure if this is a red herring or not, but I used to work for a unit that had some very old trucks (15 years at the time), and the vinyl dashboards in them were decaying into (tan/brown) powder just as you described (we figure it started due to sun exposure and crappy 70s manufacturing processing). Unfortunately we could do nothing except duct tape over the rot, and eventually we got rid of the trucks so I have no working solution for your jacket.
Was the jacket left in the back seat of a car or in sunlight for a very long time? Sunlight will decay many organic and synthetic fabrics.
I’m thinking the material might be cellulose. Rayon and Acetate are both wholly or mostly cellulose. If the jacket originally had a cotton-like feel to it, I’d guess rayon.
This site has helpful instructions on how to identify an unknown fabric with burn tests and common household chemicals:
http://www.fabrics.net/fabricsr.asp
My old '76 Nova had a red and black plaid seat-cover, can’t remember which, but one of the fabrics rotted away leaving me with kind of an egg-crate effect for seat-covers.